1. Field of the Invention
The present invention relates to a connector for optical fibres. More specifically, the invention relates to a connector for optical fibres and a device for connecting one or more optical fibres to a respective connection component. The invention also relates to a fibre-optic communication line comprising the connector of the invention and to a distribution network comprising at least two fibre-optic communication lines of the invention.
2. Description of the Related Art
Throughout the present description and the subsequent claims, the term “connection component” will be used to generally indicate an optical component, such as for example an optical fibre or a lens, or a opto-electronic components, such as for example an optical source (laser) or a photo-detector (or photo-receiver or photo-diode). For the sake of simplicity, henceforth reference will be explicitly made to the optical connection between optical fibre and opto-electronic component, i.e. a device which carries out an optical-electrical and/or an electrical-optical conversion, such as an optical source or a photo-detector, respectively; the same principles can, however, be applied to the case of a connection between two optical fibres, or between an optical fibre and a lens.
As known, in the field of telecommunications, optical technology is currently used mainly for long-distance transmission of optical signals using the known properties of wide band provided by optical fibres. However, the research is moving towards the possibility of using optical technology also in the signal distribution networks from a common branch point to a plurality of user apparatuses (such as, for example, television and/or analogue and/or digital telephone signals) and for transmitting digital data between electronic equipments (such as, for example, the Personal Computers of a LAN network), in place of the commonly used electrical cables, such as, for example, coaxial or copper duplex cables.
Indeed, electrical cables have a relatively narrow band and they are becoming a bottleneck with respect to the band of signals to be transmitted. Moreover, they exhibit problems of electromagnetic interference, of impedance matching and they are difficult to be inserted into the appropriate raceways of a building since they are stiff. In addition, being bulky, they significantly reduce the number of cables which can be inserted into a raceway. Moreover, due to electrical safety requirements, they require the arrangement of separate raceways from those used for distributing electrical energy. Differently, fibre-optic cables are suitable for being inserted into the appropriate raceways of a building since they are not too bulky, they are flexible, light, free from electromagnetic interference and they have low bending losses. In addition, they are suitable for being inserted into the same raceways which are used for distributing electrical energy. Moreover, optical fibres have a potentially very large band, low attenuation values and they are transparent to the bit rate, to the format and to the transmission code.
The connection of an optical cable to an optical source and/or to a photo-detector is conventionally carried out by means of an optical connection device. Typically, an optical connection device is a device comprising two parts (henceforth referred to as connector and receptacle) which can be repeatedly connected to and disconnected from each other and which must be attached to one end of the optical cable and to the optical source or the photo-receiver, respectively.
In the specific case of mutual connection between two optical fibres, each of the two fibres is associated with a respective connector and the optical coupling is achieved by mutually connecting the two connectors by means of an intermediate connection element. Throughout the present description and the subsequent claims, the term “receptacle” is to be understood to include also such an intermediate element.
For example, an optical cable installation suitable for connecting, inside a building, a user apparatus to a central distribution apparatus (located, for example, in an office or in a flat and, respectively, in the cellar or in the loft), requires the implementation of the following steps: passing the optical cable along an appropriate raceway in the building; cutting the optical cable according to the desired length; clamping two connectors to the two ends of the cable, in the proximity of the user apparatus and of the central apparatus, respectively; optionally clamping the optical source and/or the photo-detector (if the optical source and the photo-detector are not already provided in appropriate receptacles) to two receptacles, in the proximity of the user apparatus and of the central apparatus, respectively; and, finally, connecting each optical connector with the respective receptacle for removably connecting the optical fibre with the source and/or the photo-detector, in the proximity of the central apparatus and of the user apparatus, respectively.
Connectors for optical fibre are known in the art. Some of these connectors are disclosed in the prior art documents discussed in the patent application No. WO 03/014791 of the same Applicant.
As disclosed in WO 03/014791, a drawback associated with these known connectors is that the end portion of the fibre intended to be coupled always protrudes from the fiber supporting element for a predetermined length, also when the connector is not associated with the receptacle. Particularly during the connector maintenance operations and during the initial steps for connecting the connector to the receptacle, such an end portion of fibre is particularly exposed to possible knocks or contamination, which can cause damage and/or breaking of the fibre.
In order to overcome such a problem, WO 03/014791 of the same Applicant discloses a connector equipped with a protection cover adapted to slide, without ever coming into contact with the bare fibre, between a first position, wherein the fibre is housed inside the cover, and a second position, wherein an end portion of bare fibre is completely uncovered (i.e. directly accessible from any direction) and thus ready to be optically coupled. Advantageously, the presence of the slidable cover protects the bare fibre from possible knocks or contamination which can cause damage or breaking of such a fibre during the steps of connecting the connector to the distribution network.
However, Applicants have remarked that a drawback associated to the connector of WO 03/014791 is that, when the connector is not inserted into the receptacle, the end portion of the fibres projecting from the main body, while protected by the cover, is not supported. The length of the fibre end portion projecting from the connector is predetermined to provide also an excess of fibre with respect to the length which is strictly necessary to realise the optical connection, in order to cause the fibre to slightly arch when this come into contact with the active surface of the connection component thus generating a force which keeps the fibre pressed against the active surface of the connection component. The required projected end portion of optical fibre can be even of 10 mm in length. This end portion of fibre can be subjected to bending or inflection and/or oscillation, which can cause problems of efficiency as well as breaking of the fibre, especially if micro-cracks exist in this portion of fibre.
EP 0 969 298 discloses a connector for optical fibres comprising an outer member including a clamping element for clamping an optical fibre bunch, a fibre supporting member for holding a portion of optical fibres remote from their connecting end and an aligning member which is held by the outer member so as to be movable along the optical fibres. The aligning member carries out positioning of the connecting end of the optical fibres. The aligning member is urged by a spring in a direction to project from the outer member. Connection of each optical fibre of the connector to a counterpart optical fibre is carried out by connecting the connector to a receptacle housing the counterpart optical fibre. When connecting the connector to the receptacle, the aligning member is moved in a direction opposite to the foregoing direction against the urging force applied by the spring so that the connecting end of the optical fibre is projected from the aligning member.